Fix project thumbnail upload update and persistence on reload

[Copilot]

Description of changes

Fixes issues where uploading a new project thumbnail did not update the table immediately and failed to persist on page reload.

• Immediate table updates: Changed the thumbnail column accessor in useProjectColumns.ts from name to updatedAt. This triggers a React Table re-render of the cell when the thumbnail is updated. ProjectThumbnailCell.tsx was adjusted to read projectName from the row's original object instead of the cell value.
• Persistence on reload: Fixed caching in ProjectDetailsPanel.tsx. The initial updatedAt value is now only captured once project data is loaded, ensuring the proper date is appended to the thumbnail URL query string to bust the browser cache.

Technical details

• The thumbnail column was previously not reacting to updatedAt changes because the name accessor value didn't change on upload.
• thumbnailUpdatedAtRef.current was inadvertently being set to undefined during the initial loading state before data was fetched, causing subsequent image requests to omit the cache-busting updatedAt parameter.

Additional context